1. Field of the Invention (Technical Field)
The present invention relates to sensors and actuators, and more particularly to polymeric materials and the fabrication processes for solid state polymeric sensors and actuators.
2. Background Art
Polymeric devices that can directly convert electric energy to mechanical energy (electromechanical effects) have attracted a great deal of attention in recent years. The definite advantages of such polymeric devices originate from their soft mechanical properties (inherently polymeric behavior) that have a significant potential to mimic various biological situations necessary to enhance human activities and/or serve as special industrial actuators. A number of prior art materials in this category recognized so far include: i) conducting polymers, E. Smela, O. Inganas, I. Lundstrom, Science 268, 1735 (1995); T. F. Otero, J. Rodriguez, E. Angulo, C. Santamaria, J. Electroanal Chem. 341, 369 (1992); A. Della Santa, D. De Rossi, A. Mazzoldi, Synthetic metals, 90, 93 (1997); M. R. Gandhi, P. Murray, G. M. Spinks, G. G. Wallace, Synth. Met. 73, 247 (1995); A. Mazzoldi, D. De Rossi, Proceedings of SPIE-Electroactive Polymer Actuators and Devices (EAPAD) 3987, 273 (2000); ii) ferroelectric polymers Q. M. Zhang, V. Bharti, X. Zhao, Science 280, 2101 (1998); J. Lovinger, Science 220, 1115 (1983); iii) ionic polymer metal composites M. Shahinpoor, Y. Bar-Cohen, J. O. Simpson, J. Smith, Smart Mater. Struct. 7, 15 (1998); P. G. De Gennes, K. Okumura, M. Shahinpoor, K. J. Kim, Europhysics Letters 50, 513 (2000); K. Asaka, K. Oguro, Y. Nishimura, M. Mizuhata, H. Takenaka, Polym. J. 27, 436 (1995); and iv) ionic polymeric gels R. Hamden, C. Kent, S. Shafer, Nature 206, 1149 (1965); T. Tanaka, I. Nishio, S. Sun, S. Ueno-Nishio, Science 218, 467 (1982); Y. Osada, H. Okuzaki, H. Hori, Nature 355, 242 (1992); M. Doi, M. Matsumoto, Y. Hirose, Macromolecules 25, 5504 (1992).
Conducting polymers can become electromechanically active via electrochemical dopant intercalation in the redox material. Although the predicted force/power generation capability of conducting polymers are high, development efforts are hampered due to rate-limiting interfacial dopant diffusion and, therefore, cost their lifetime and thermodynamic efficiency. Also, its operation in dry environments is possible but not effective to create useful strain for appropriate engineering applications. Ferroelectric materials such as poly(vinyliedene fluoride-trifluoroethylene, PVDF-TrFE) copolymer are recently recognized as giant electrostriction and relaxor and operational in dry environments but require very high electric field (>10 kV/mm) for an appropriate range of actuation capabilities to attract engineering applications. Ionic polymer metal composites in a form of a strip show a large bending capability under a small electric field (<10 V/mm) along with considerable forces and fast responses. However, the operation of these devices is effective only in wet climates, therefore, the engineering applications are limited to wet environments. Ionic polymer gels, such as PVA fibers and polyacrylamide, can also show electromechanical behavior. Ionic currents create local ion exchanges so as to alter the osmotic pressure in polymer gels, i.e., Donnon exchange. However, such ionic polymer gels suffer from their weak mechanical strength and consequent microfractures upon large deformations and result in short life span materials.
The present polymer solid-state actuators overcome many inherent problems that other state-of-the-art polymer actuators have, such as rate limiting dopant intercalation of conducting polymers, high voltage requirement of ferroelectric polymers, favorable wet conditions of ionic polymer metal composites, and poor mechanical properties of ionic polymeric gels. Therefore, the disclosed solid-state polymer actuators and sensors have tremendous potential for use in biomimetic/medical, industrial, and domestic applications than the present prior art polymer materials.